Atmospheric science and weather forecasting require measurements of the temperature and humidity vs. altitude. These sounding measurements are obtained at frequencies close to the resonance frequencies of oxygen (118 GHz) and water (183 GHz) molecules. We have characterized a broadband amplifier that will increase the sensitivity of sounding and other instruments at these frequencies. The measured InP monolithic millimeter-wave integrated circuit (MMIC) amplifier had more than 18 dB of gain from 100 to 180 GHz and 15 dB of gain up to 220 GHz. This is the widest bandwidth low noise amplifier result at these frequencies to date. The circuit was fabricated in Northrop Grumman Corporation 35 nm InP high electron mobility transistor (HEMT) process. The typical microwave sounding satellites use primarily the 60 GHz oxygen line for temperature sounding, however, there are several advantages to be gained from observations near the 118.75 GHz oxygen line. For fixed aperture dimensions, a diffraction-limited 118 GHz system will yield twice the spatial resolution of a similar 60 GHz system. Additionally the sensitivity to clouds and precipitation at 118 GHz is typically greater than at 60 GHz. This greater sensitivity to hydrometeors enables improved detection of regions of heavy cloud and precipitation relative to that available using 60 GHz frequency window or sounding channels. The frequency channels in the proximity of 183 GHz are used for atmospheric sounding of water vapor.